Operational amplifier designs have always been limited in that conventional PNP integrated circuit transistors used therefor can operate only to around 5 megahertz. These PNP transistors in combination with conventional NPN transistors are typical devices found in operational amplifier integrated circuits.
Recently, a high-frequency isolated vertical PNP (VPNP) transistor has been developed that is superior to the conventional and substrate PNP transistors. This isolated VPNP transistor is capable of 45-volt operation and exhibits a maximum operating frequency around 150 megahertz. The current gain and breakdown voltages on the isolated VPNP transistor are comparable to those achieved on the standard double diffused NPN transistor. Finally, the isolated VPNP is not limited to the emitter-follower configuration taken by the normal vertical substrate PNP transistor.
Separately, a 50-volt (p) channel JFET has been developed to extend the gate-to-drain breakdown voltage past 45 volts. JFETs of this kind are conventionally used as operational amplifier inputs. These JFETs are achieved by using a thick deposited oxide over the gate oxide to reduce the electric field intensification at the top gate/drain reverse-biased p-n junction. This increases the gate-to-drain breakdown voltage from the low 30 volt range to approximately 50 volts. The gate-to-drain and gate-to-source oxides overlap capacitances are also reduced with the deposited oxide. This contributes to higher bandwidths and slew rates.
Another desirable integrated circuit component is the metal/nitride/poly capacitor. The use of nitride in the place of oxide provides a doubling of the capacitance and allows for a dielectric breakdown in excess of 100 volts, and the fabrication of these capacitors on field oxide reduces parasitic junction capacitance and tank leakage currents.
It is therefore desirable to develop a process for the fabrication of an integrated circuit including each of these devices. As yet, no such process has been heretofore developed, limiting circuit designers to the use of one of these circuit devices without the others in any one integrated circuit.